In relation to porous refractory materials (melting assemblies) suitable for glass production, various problems usually arise upon contact with a molten glass. On the one hand the corrosion rate of the surface of the refractory material is directly proportional to the area of contact with the molten glass so that penetration of the molten glass into the generally open porosity of the refractory material results in an increase in corrosion. Besides that reduction in the service life of the melting assembly in addition refractory material can involve dissolution or partial dissolution on the surface in relation to the pore volume, which is then mixed with the molten glass which penetrates into the pores and can thus result in production disturbances, for example inhomogeneities or cords in glass production, as an unwanted accompanying phenomenon. In addition, when the molten glass penetrates into the pore volume of the refractory material, the gaseous phase therein can be at least partially absorbed into the molten glass, which for example can lead to the inclusion of bubbles and thus further production disturbances in glass production (Glastechnische Fabrikationsfehler, Jebsen-Marwedel, R Buckner: Springer-Verlag 1980, page 263).
In order now to improve the corrosion resistance of refractory materials in glass production the surface of the refractory material can be refined and improved by the construction of resistant layers (US No 2003/0104196 and EP 0 911 298) or by coating with platinum metals (GB 211 530 and WO 99/23050). A disadvantage in that respect is on the one hand the high level of complication and expenditure for surface refining and on the other hand the reduced corrosion resistance as soon as the respective layer is worn out.
U.S. Pat. No. 3,670,061 describes a method of improving the corrosion resistance of refractory materials, wherein the refractory material is melted and dry gas is specifically and targetedly introduced into that molten material to produce reduced porosity and concomitantly therewith improved corrosion resistance of the refractory material.
DE 23 11 306 describes a method of increasing the durability of a refractory brickwork of metallurgical vessels by the incorporation of carbon during ongoing operation, wherein a fluid carbon carrier is infiltrated into the brickwork in situ from the undestroyed side of the brickwork.
DE 199 36 292 describes a refractory shaped body for metallurgical processes, a corresponding compound and the production process for same, wherein the refractory material has a high level of resistance in relation to slags of the most widely varying compositions, in particular with different or changing pH values with at the same time handling without any problems and disposal without any problems. That refractory material as the main component comprises a mineral oxidic material which is chemically composed of between 80 and 99% of Al2O3 and between 1 and 20% of CaO, wherein the mineral oxidic material of the brick which is ready for use has a phase mixture of α-Al2O3, β-Al2O3, calcium hexaaluminate (CA6) and calcium dialuminate (CA2) which can be included in proportions respectively between 2 and 50%, preferably respectively between 20 and 30%.
The technical objects on which the present invention is especially based provide for the provision of a porous refractory material suitable for glass production, which has improved corrosion resistance in relation to a molten glass, which permits a reduction in production disadvantages in glass production, which in particular allows a reduction in impurities and contamination in the glass produced, and which is to be produced inexpensively and with simple means.